The draft apparatus is indispensable for a spinning frame and according to the conventional drafting method, drafting is gradually accomplished through the roving step and the subsequent spinning step. We, the applicants of the present application, have invented a novel high draft apparatus comprising back rollers, apron-provided middle rollers and front rollers being arranged in succession along a yarn passage, in which the roving step is omitted.
In a drafting device of the above-mentioned type, a driving power for the drafting device is transmitted through reduction gears and the like from a driving motor for driving take-up rollers and friction rollers in common. In this drafting device, speeds of back rollers, middle rollers and front rollers are changed through reduction gears and the like according to the draft ratio, and these rollers are co-operatively rotated.
The middle rollers disposed in the above-mentioned drafting device are provided with an apron for controlling the draft unevenness, and non-uniform rotations and vibrations are more readily caused in the middle rollers by influences of the apron than in other rollers. In the high drafting device, the influences of the apron are especially serious because the rotation speeds are high. If non-uniform rotation and vibration are thus caused in the middle rollers, these non-uniform rotation and vibration are propagated to the back rollers and front rollers rotated co-operatively with the middle rollers, and bad influences are imposed on the properties of spun yarns, such as the yarn evenness and tenacity. Since the front rollers are rotated at a higher speed than other rollers, the front rollers are very readily influenced even by very slight non-uniform rotation or vibration propagated thereto.